A Comparative Study of Certain Biological Phenomena Detected in a Parathion-Treated Strain and a Susceptible Strain of the Plum Curculio, Conotrachelus nenuphar1

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Abstract
An investigation was conducted to study the development of resistance to parathion, the cross tolerance responses of the resistant strain to certain toxicants, and biological differences between a laboratory reared resistant strain and a susceptible strain of the plum curculio, Conotrachelus nenuphar (Herbst). A strain was selected for resistance to parathion by applying this chemical topically to the insects. The susceptibility of the resistant-selected strain to parathion was determined by topical application to each generation for seven generations and cross tolerance of the strain to other toxicants was determined for the third and seventh generations. Insecticides used were parathion, Guthion® (O,O-dimethyl S-(4-oxo-1,2,3,-benzotriazin-3(4H)-ylmethyl) phosphorodithioate), dieldrin, and Sevin® (1-naphthyl N-methyl carbamate) representing two phosphates, a chlorinated hydrocarbon and a carbamate insecticide, respectively. There was a slow irregular increase in tolerance to parathion. The response to Guthion and dieldrin increased similarly to parathion. There was an initial icrease in susceptibility to Sevin followed by a decrease to the original level of tolerance for the seventh generation. The most significant differences found in the biological investigations were au increase in the length of the embryonic and larval periods and a decrease in the preoviposition period which resulted in no differences in the egg to egg cycle. The fecundity, estimate of vigor and length of adult life all decreased significantly from that of the susceptible strain but by the seventh generation, all were comparable to the susceptible strain. No differences were observed for length of pupal development, sex ratio or adult weight.

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